The present invention relates to optical connector ferrules which can be used in optical fiber connectors for use in optical fiber communication circuits. Optical connector ferrules can also be used in optical attenuators of the variable attenuation type which resemble the optical fiber connectors in structure.
For an optical connector ferrule used to connect an optical fiber to another optical fiber, it is well known by the ordinary person skilled in the art that the normal to the circular surface at the edges of the optical fiber and optical connector ferrule which is used to connect the optical fiber to another optical fiber has to be seven degrees or more with respect to the optical axis of the optical fiber so that the optical losses caused by reflection of an optical beam at the interface between the optical fiber edge and the other surface might be minimized because the optical beam reflection makes the optical power losses increase during the optical power transmission.
If the surface at the edges of the optical fiber and optical connector ferrule is hemispheric and at right angles with respect to the optical axis of the optical connector ferrule through which the optical power can pass, it is also well known by the ordinary person skilled in the art that the optical power losses caused by reflection of the optical power at the interface between the optical fiber edge and the other surface will decrease provided that the polished circular surface of the optical connector ferrule is faced to the other surface at right angles.
FIG. 1 shows an example of an optical connector ferrule body used for conventional optical communications.
Tapered connecting section 3 is provided at an edge of a cylindrical ferrule body 1 made of metal and hole 2 is bored through the optical axis of cylindrical ferrule body 1 so that an optical fiber can pass through the cylindrical ferrule body 1.
The tapered connecting section 3 is provided so that a pair of ferrules might smoothly be inserted into an alignment sleeve which aligns the paired ferrules to be inserted from opposite sides of the alignment sleeve, and so that the inner surface of the alignment sleeve might not be cracked during the attachment/detachment of the optical fibers.
Tapered connecting section 3 is approximately 30 degrees inclined to the optical axis of the cylindrical ferrule body 1.
It is well known by the ordinary person skilled in the art that the surfaces at the edges of the ferrule body and optical fiber can be made hemispherical by simultaneously polishing these surfaces. The hemispheric surface at the edges of the ferrule body and optical fiber can be obtained by the inclined hemispheric polishing of the surface on an elastic material disk when the surface is inclined with respect to the elastic material disk because of their circular deflection.
The method of polishing which is well known by the ordinary person skilled in the art is such that a polishing film is arranged on an elastic material disk so that the edges of the ferrule and optical fiber loosely touch the elastic material disk and such that the edges of the ferrule and optical fiber move against the elastic material disk surface as the disk rotates.
FIG. 2 shows a cross sectional view of an example of the edges of the optical fiber and ferrule materials whose surface is made hemispheric by the use of the polishing film.
Polishing film 7 is attached onto the surface of elastic material disk 6 through an adhesive agent. Polishing tool 8, wherein hole 5 inclined to the normal to the elastic material disk by a predetermined angle .theta., is provided so that the edge of the optical connector ferrule is set at .theta. degrees with respect to elastic material disk 6. When elastic material disk 6 rotates, the edges of the ferrule and optical fiber move around a circle on the elastic material disk 6 while touching polishing film 7 attached on the surface of the elastic material disk 6.
The vertex on the hemispheric surface being polished has to lie on the optical axis of the optical fiber during the polishing to form an inclined hemispheric surface at the edges of the optical fiber and ferrule.
In accordance with the specifications, the offset of the center of the hemispheric surface to the optical axis of the optical fiber should be 0.06 mm or less when the radius of curvature for the hemispheric surface is 10 to 20 mm. In accordance with the above method, the finished surface satisfies the specifications described above although tapered connecting section 3 provided at the edge of the optical connector ferrule mainly determines the offset of the vertex on the hemispheric surface to the optical axis of the optical fiber.
How to solve the above problem will be described hereinafter referring to an example wherein a ferrule body with a tapered connecting section is inclined by an angle .theta. during polishing.
FIG. 3 shows an enlarged view of the optical connector ferrule edge being polished in accordance with the above-mentioned polishing method.
In accordance with this polishing method, the optical connector ferrule is finished in such a manner that the outer edge thereof can concentrically be rubbed off, and vertex P on hemispheric surface R becomes the central point of the distance between points A and B.
The quantity of the materials scrubbed from the optical fiber and optical connector ferrule at point B is greater than that scrubbed from the optical fiber and optical connector ferrule at point A, and point P shifts toward point B by a distance S starting from point O on the optical axis of the optical fiber.
Distance S increases as the angle .theta. of the inclination increases. The radius of curvature of the hemisphere increases as the quantity of the materials scrubbed for the optical fiber and optical connector ferrule increases because the pressure of the scrubbing decreases in inverse proportion the quantity of materials scrubbed from the optical fiber and optical connector ferrule. Any change in the radius of curvature of the hemisphere is thus not fixed and uncertain.
If an optical connector ferrule having a tapered connecting section at the edge thereof is finished by scrubbing the edge thereof in such a manner that the hemispheric surface at the edge of the optical connector ferrule is at any other than a right angle or inclined with respect to the optical axis of the optical fiber when the edge of the optical connector ferrule has been polished, the conditions of how the polishing is performed depend on how the optical connector ferrule edge has been scrubbed. The performance of connecting a pair of optical fibers together depends on the radius of curvature of the hemispheric surface after the polishing is completed and on the roughness of the hemispheric surface at the edge of the optical connector ferrule.
The quantity of the materials scrubbed from the optical fiber and optical connector ferrule edges in such a manner that the normal to the optical fiber and optical connector ferrule edges is inclined with respect to the optical axis of the optical fiber in the ferrule body by an angle .theta. is 10 times or more greater than that scrubbed from the optical fiber and optical connector ferrule edges in such a manner that the optical fiber and optical connector ferrule edges are at a right angle with respect to the optical axis of the optical fiber in the ferrule body. Thus, the finishing of the optical fiber and optical connector ferrule edges when the edges thereof are inclined consumes a much greater time than when the edges thereof are at right angle with respect to the optical axis of the optical fiber. Greater time to finish the optical fiber and ferrule edges degrades the performance thereof because the optical fiber edge sometimes burns due to the abrasion. How to reduce the quantity of the materials scrubbed from the optical fiber and optical connector ferrule is of great importance.
The objective of the invention is to present a different type of optical fiber ferrule which can be used to construct an optical fiber connector for use in optical fiber communication equipment, and to construct an optical attenuator of the variable attenuation type which resembles an optical fiber connector.